This invention relates to magnetic heat pumps. Specifically, the invention is a rotary magnetic heat pump used to pump heat energy from a low temperature source to a high temperature sink. The invention also contemplates use as a refrigerator usable to remove heat from a source and pump it into a sink. The term heat pump will be used to indicate both refrigerators and heat pumps hereinafter.
Magnetic heat pumping involves expulsion of heat into a high temperature sink from the magnetic working material through the application of a magnetic field. Subsequent removal of the magnetic field increases entropy of the working material and allows absorption of heat from a low temperature bath. Magnetic refrigerators and heat pumps operate near the ferromagnetic Curie temperatures of working materials and with proper selection of working materials can work at any temperature range from near absolute zero to near 1400 degrees Kelvin. As known in the art, different materials have different Curie temperatures.
At temperatures above 20.degree. Kelvin, in order to obtain useful temperature increases through magnetic heat pumps and to achieve good thermal efficiency it is necessary to use recuperation or regeneration to preheat the working material before magnetization and cool the material before demagnetization. Past attempts to build regenerative or recuperative magnetic heat pumps have included reciprocating designs and rotary designs.
Reciprocating devices, such as that shown in U.S. Pat. No. 4,459,811 and U.S. Pat. No. 4,332,135 have intrinsic problems with regenerator fluid mixing and reduced efficiency since regenerator fluid must change temperatures to store energy. The major problem with building practical rotary designs is devising a method to pump recuperator fluids through a moving wheel. Previous rotary magnetic heat pumps utilized seals in the wheel or housing and/or segmented wheels to accomplish the pumping of heat transfer fluid through the rotating working material. The seals and segmented wheels of previous designs add complexity, do not work well and the added friction and fluid leakage which degades performance significantly detracts from the commercial useability. Frictional heating in the recuperative portions of the wheel is especially detrimental to good thermodynamic performance of magnetic heat pumps.
For example, U.S. Pat. No. 4,107,935, issued to Steyert discloses a rotary magnetic refrigerator using a wheel segmented into spaces through which heat transfer fluid flows radially in the segments, back and forth. The spacing between the housing and the segmented wheel is "of the order of a few thousandths of an inch" to prevent "any significant flow" of fluid between the rim of the wheel and flow separators forming the wheel segments. The relatively complex design of the segmented wheel and close tolerance fit with the housing limits the practical useability of the refrigerator disclosed. A simpler design, eliminating the segmented rotor and the need for a close fit or fluid seals would be a substantial improvement over existing rotary magnetic heat pump designs.
Accordingly, it is an object of the present invention to provide a magnetic heat pump.
Another object of the invention is to provide a rotary magnetic heat pump.
Another object of the invention is to provide a rotary magnetic heat pump utilizing regeneration and recuperation without the use of cross-flow rotor design or fluid seals.
Yet another object of the invention is to provide a rotary magnetic heat pump eliminating the requirement of seals on the rotor and/or cross-flow rotor design and provide a Carnot efficiency in excess of 70%.
Additional objects, advantages and novel features of the invention will be set forth in part in the description which follows, and in part will become apparent to those skilled in the art upon examination of the following or may be learned by practice of the invention. The objects and advantages of the invention may be realized and attained by means of the instrumentalities and combinations particularly pointed out in the appended claims.